The present invention relates generally to cannon ammunition and other projectiles, and more specifically to an insert assembly that adds a spotting charge to normally non-explosive shells.
Air Force AC-130 gunship weapons include a 40 mm Bofors cannon. For most military operations, the cannon fires a high explosive incendiary shell.
Such high-explosive incendiary shells are in both short supply and expensive, severely limiting their use for training.
There is a large supply of surplus World War II 40 mm armor-piercing rounds that are used for training, but because they don't contain any explosive, it is difficult to visually determine ground strikes. Without an impact signature, aircrews and ground crews cannot assess shot placement and correct the fire control system for errors.
There is a large prior art of so-called spotting charges for use in training and practice projectiles, both projectiles designed and built specifically for those purposes and for retrofit units used to convert normally non-explosive shells, such as so-called dummy warheads, to spotting charge projectiles.
A careful search of the prior art reveals that all these prior art spotting charges use complex mechanisms to trigger or ignite the spotting charge or other explosive or incendiary material used for creating a visual or audible, or both, effect. The prior art need for such complex mechanisms is because typical incendiary materials and mixtures will normally only initiate or ignite on hard impact or under a heavy shear.
Those mechanisms typically include a penetrator or similar component that, when the projectile strikes a surface, shoots forward to ignite a primer charge to then ignite the spotting charge. These mechanisms are usually very similar to those used to ignite both primer (or percussion) and main charges in regular explosive shells.
The simplest mechanism found in the prior art is that described in U.S. Pat. No. 4,488,490 to Betts. The Betts spotting charge is designed for use with a solid propellant rocket. A percussion primer material fills a cavity in the front of the rocket and ignites from the impact of the rocket striking a hard target. The pressurized hot gases from the percussion primer are communicated through a bore behind the cavity to the pyrotechnic spotting charge.
While the Betts spotting charge is a clear improvement in simplicity over the other prior art, it is limited to use with hard targets.
Typical gunship targets, in addition to hard surface targets, include soft surfaces such as vegetation and ground.
It is seen, therefore, that there is a need for new and simpler solutions, and thus less expensive, for the prior art problem of adding a visual and audible impact signature for non-explosive containing ammunition and other projectiles.
There is a particular need for new and simpler solutions that will work for impacts on soft, as well as hard, surfaces.